SEATAC, Wash. — Masked thieves driving two vehicles blocked in gem couriers on a highway ramp near SeaTac and stole $400,000 worth of diamonds from their car.

The King County Sheriff’s Office says the heist happened around noon Tuesday. The victims were in the Seattle area from Hong Kong to sell diamonds.

The sheriff’s office said Thursday that the driver and passenger, employed as diamond couriers, were driving on a ramp to Interstate 5 when a black car cut them off and stopped in front of them. Meanwhile, another car struck them from behind.

Two men wearing masks and sunglasses approached the couriers, assaulted the driver, broke out two car windows and stole a backpack containing diamonds worth over $400,000. They drove off.

One witness told police a third suspect pointed a handgun at the victims while the other two robbed them. One of the suspects punctured the tires of the victims’ car.